US3718162A

US3718162A - Circuit breaker

Info

Publication number: US3718162A
Application number: US00196010A
Authority: US
Inventors: G Dafler; L Magyar
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1971-11-05
Filing date: 1971-11-05
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27

Abstract

In a preferred form, this disclosure relates to an overload circuit breaker having a metal base with an upwardly extending tang thereon, a stationary contact carried by, but insulated from the base, a bimetal strip including a primary U-shaped portion having one leg carrying a mobile contact adjacent its free end and overlying said stationary contact and a secondary portion supported in cantilever fashion by the tang and having its free end connected with the other leg of the U-shaped primary portion. The bimetal strip is normally self-biased toward a first position in which the mobile contact engages the stationary contact to provide a conductive path therethrough, but is movable toward a second position in which the mobile contact is disengaged from the stationary contact when a current in excess of a predetermined magnitude is passed therethrough for a predetermined interval of time. The tang on the base is bendable to adjust the spring pressure of the bimetal strip so that the predetermined time interval prior to opening of the contacts when an overload of current is passed therethrough can be readily calibrated.

Description

United States Patent [19] Butler et al.

1 Feb. 27, 1973 1 CIRCUIT BREAKER [75] Inventors: Gene L. Dafler, New Lebanon; Lorand W. Magyar, Dayton, both of [58] Field of Search ..337/94, 95, 96, 99, 101, 111, 337/349, 372, 374, 375, 379

[56] References Cited UNITED STATES PATENTS 3,292,070 12/1966 Hischak ..337/111 UX 2,794,884 6/1957 Shaw et a1. ..337/96 3,288,967 11/1966 Perry ..337/94 X 3,238,780 3/1966 Doyle ..337/379 X 2,627,003 1/1953 Porter ..337/94 UX Primary ExaminerHarold Broome Assistant ExaminerA. T. Grimley Attorney-W. E. Finken et al.

[57] ABSTRACT In a preferred form, this disclosure relates to an overload circuit breaker having a metal base with an upwardly extending tang thereon, a stationary contact carried by, but insulated from the base, a bimetal strip including a primary U-shaped portion having one leg carrying a mobile contact adjacent its free end and overlying said stationary contact and a secondary portion supported in cantilever fashion by the tang and having its free end connected with the other leg of the U-shaped primary portion. The bimetal strip is normally self-biased toward a first position in which the mobile contact engages the stationary contact to provide a conductive path therethrough, but is movable toward a second position in which the mobile contact is disengaged from the stationary contact when a current in excess of a predetermined magnitude is passed therethrough for a predetermined interval of time. The tang on the base is bendable to adjust the spring pressure of the bimetal strip so that the predetermined time interval prior to opening of the contacts when an overload of current is passed therethrough can be readily calibrated.

3 Claims, 5 Drawing Figures CIRCUIT BREAKER The present invention relates to an overload circuit breaker, and in particular to an overload circuit breaker which can be readily calibrated.

It has been common to employ thermal overload circuit breakers in automotive electric motors, such as windshield wiper motors, and with the overload circuit breaker being connected in circuit with the motor so that the total motor current flows therethrough. Such an overload circuit breaker is disclosed in Wood US. Pat. No. 2,585,068, which circuit breaker is responsive to both ambient temperature and motor current.

The primary function of an overload circuit breaker in an electric motor is to protect the motor from destruction due to excessive heat under a stall condition. The overload circuit breaker setting is determined and calibrated by tests under stall conditions of the motor. It is well recognized that commercially available thermal overload circuit breakers cannot be economically calibrated to open at a precise time interval due to production methods and tolerances of the various parts, and accordingly, commercially available overload circuit breakers have a spread of a predetermined time interval between low and high limit trip times, which spread may be on the order of 6 to 8 seconds.

One common type of overload circuit breaker which has heretofore been used is like that disclosed in Wood U.S. Pat. No. 2,585,068, a circuit breaker which is responsive to both ambient temperature and motor current. This type of circuit breaker included a metal base, a stationary contact carried by, but electrically insulated from the base, and a two-piece bimetallic member having a primary U-shaped portion having one leg carrying a mobile contact adjacent the free end and overlying the stationary contact and a secondary portion supported in cantilever fashion by the base and having its free end welded to the other leg of the U- shaped primary portion. The bimetal was self-biased so that the upper U-shaped portion tended to keep the contacts closed. When an overload current condition existed the upper bimetal tended to open the contacts, but the lower bimetal member deflected to keep the upper one closed initially during the overload until a predetermined time period passed whereby the upper one would deflect to open the contacts. The secondary portion, since it was connected to the metal base tended to cool more rapidly and to deflect toward its normal c001 position and thereby tended to keep the upper bimetal in a position in which the contacts were open for a predetermined time period before the bimetal cooleddown and again closed the contacts. This time period was for approximately 10 seconds.

The above-noted type of circuit breaker, to be functional with specific types of motor applications, must operate to separate the contacts within a predetermined time interval, between low and high trip time, (16 to 22 seconds in windshield wiper motor applications). Due to production methods and the tolerance variations within individual circuit breakers being manufactured it is necessary to calibrate the bimetal strip. To calibrate the bimetal strip it was heretofore necessary to push either the primary or secondary bimetal portion down to a certain force level and prediet that it would open within a certain time interval when an overload current was passed therethrough. If it did not open within a time interval, it was necessary to readjust the spring pressure by deflecting or deforming either one of the bimetal portions until the desired time interval was achieved. This method of calibrating the circuit breaker is both costly and not highly accurate.

The present invention relates to a new and improved overload circuit breaker of the above-noted type and which has less tolerance problems and better predictable heat flow characteristics than known circuit breakers of this type and can be readily and accurately calibrated.

Accordingly, an important object of the present invention is to provide a new and improved overload circuit breaker of the kind referred to above and in which the bimetal strip is supported in cantilever fashion on a tang or lever extending outward from the plane of the base and in which the tang is bendable while the breaker is being calibrated by passing an overload current therethrough to cause the bimetal strip to disengage its associated stationary contact adjacent the start of the time interval whereby subsequent use of the circuit breaker will cause the bimetal strip to open within the predetermined time interval.

Another object of the present invention is to provide a new and improved circuit breaker, as defined in the preceding object, and in which the bimetal strip is of a one-piece construction.

A further object of the present invention is to provide a new and improved method for calibrating a circuit breaker of the type referred to above which includes the steps of supporting the bimetal strip on an upwardly extending tang on the base, passing an overload current therethrough, and pushing down on the tang at the predetermined time subsequent to the start of the overload current passing thercthrough to cause the bimetal strip to open the contacts adjacent the start of the predetermined interval of time whereby the overload circuit breaker is accurately calibrated.

The advantages of the above overload circuit breaker are that it can be accurately calibrated to cause the contacts to open within a predetermined time interval irrespective of the tolerance variations of the various parts of the circuit breaker. By pushing down on the tang at the start of the predetermined time interval to cause the contacts to open guarantees that the circuit breaker will always open within the predetermined time interval irrespective of the spring back characteristics of the bimetal strip, since any subsequent opening of the contacts will be intermediate the range of the predetermined time interval. Other advantages are that by using a one-piece bimetal construction, a savings in material handling is achieved as well as better predictable heat flow because there is no weld between the two bimetal portions.

The present invention further resides in various novel constructions and arrangement of parts, and further objects, novel characteristics and advantages of the present invention will be apparent to those skilled in the art to which it relates and from the following detailed description of the illustrated embodiments thereof made with reference to the accompanying drawings forming a part of this specification and in which similar reference numerals or characters are employed to designate corresponding parts throughout the several views, and in which:

FIG. 1 is a top plan view of a preferred embodiment of the overload circuit breaker of the present invention;

FIG. 2 is a side elevational view looking in the direction of the arrow 22 of FIG. 1;

FIGS. 3 and 4 are side elevational views like that shown in FIG. 2, but showing different parts thereof in different positions; and

FIG. 5 is a perspective view of another embodiment of an overload circuit breaker of the present invention.

As representing a preferred embodiment of the present invention, FIG. 1 of the drawings shows an overload circuit breaker 10. The overload circuit breaker comprises a base 12 having a planar top portion 14 and depending side portion 16. The side portion 16 includes a pair of openings 18 to enable the base 12 to be bolted to a suitable support within an electric motor (not shown). The top portion 14 of the base 12 includes a section which is separated therefrom by a slot 20 and which is bent upwardly or outwardly of the plane of the base to define a tang or lever 22. The tang 22 has a first portion 22a integral with the top portion 14 of the base and which extends upwardly therefrom at an acute angle and a second portion 22b which is spaced from the plane of the top portion 14 but extends parallel thereto.

The top portion 14 of the base further carries a stationary contact 24 and a stationary male blade terminal 26. The contact 24 and the male blade terminal 26 are electrically insulated from the base by a pair of insulated

strips

28 and 30 made from a suitable electrically insulating material. The stationary contact 24 is in the form of a rivet which is staked over on the underside of the male blade terminals 26 as indicated at 32 to securely retain the stationary contact 24 and the male blade terminal 26 in place. The male blade terminal 26 is adapted to be connected to a suitable lead in the circuit for the electric motor (not shown). The stationary contact 24 has a convex upper surface 24a and is preferably made from a sliver-cadmium material.

The circuit breaker further includes a one-piece bimetal strip or member 40. The bimetal member 40 is stamped from suitable strip stock and bent to the configuration shown in the drawings. It can be made from any suitable metallic materials having different coefficients of expansion. The bimetal member 40 includes an upper or primary portion 42 and a lower or secondary portion 44. The upper portion 42 is bent into the shape of a U and has a long leg section 42a, a short leg section 42b and a bight section 42c. The long leg 420 carries a mobile contact 46 adjacent its free end which overlies the stationary contact 24. The mobile contact 46 has a convex surface 46a and is preferably made from a silver-cadmium material. The lower portion 44 is rigidly connected at one end 44a to the portion 22b of the tang 22 by a rivet 50. The lower portion 44 is substantially planar and it and the U-shaped portion 42 are supported in cantilever fashion by the tang 22. The upper and

lower portions

42 and 44 are located side by side andwith the lower portion 44 being integrally connected at its other end 44b to the free end of the leg 42b of the upper portion 42.

The bimetal member 40 is resilient and self-biased toward a first position in which the mobile contact 46 is in engagement with the stationary contact 24, as shown in FIG. 2, when at room temperature and no current is being passed therethrough. When a non-overload current of less than a predetermined-magnitude is being passed therethrough and/or the ambient temperature rises, the'upper bimetal portion 40 heats up and tends to separate the

contacts

46 and 24. However, since the lower portion 44 is also being heated it tends to move or deflect toward a position, as shown in FIG. 3. Thus, the lower portion 44 tends to maintain a constant pressure on the upper portion 42 to maintain the contacts closed with a predetermined pressure while normal currents are passed through the bimetal member.

The lower portion 44 of the bimetal 40 also keeps the upper portion 40 in its first or closed position during the initial time period when an overload condition occurs, i.e., when a current in excess of a predetermined magnitude is passing through the bimetal member 40. Thus, the lower member 44 will tend to deflect further downwardly. However, since the lower member 44 is directly connected to the base 12, heat will be dissipated by conduction much more readily than heat will be dissipated by convection when the upper member 42 heats up. Thus, at a predetermined time period sub sequent to an overload current passing through the bimetal member 40, the upper portion 42will deflect toward a second position in which the mobile contact 46 is separated from the stationary contact 24, as shown in FIG. 4.

The lower portion 44 also serves to hold the upper portion 40 in its open position, as shown in FIG. 4, for a predetermined time interval, preferably approximately 10 seconds. The upper portion 42 when in its open position will tend to cool rapidly by convection, but not as rapidly as the lower portion 44, since the lower portion 44 is directly connected to the base 12 and hence will tend to cool more rapidly due to conduction through the base. This results in the lower portion 44 cooling and deflecting upwardly to maintain the upper portion 42 in a circuit open position for a predetermined time, approximately 10 seconds.

An important feature of the present inventiori is the provision of the tang 22 which enables the spring,pressure of the bimetal member 40 to be readily adjusted during the calibration process by bending the same so that the bimetal will deflect to open the

contacts

46, 24 within a predetermined time interval subsequent to the passage of an overload current therethrough.

After the overload circuit breaker 10 is constructed and assembled as shown in the drawings, it is calibrated by connecting the base at its left end to a suitable lead and the terminal 26 to another lead in the circuit and then passing an overload current through the bimetal member 40. Assuming that the bimetal should open within a time interval of l6 to 22 seconds subsequent to the start of an overload current passing therethrough, the person doing the calibrating would merely push down on the tang 22 with a suitable tool to deflect and bend the same toward the top portion 14 of the base 12 to cause the

contacts

46 and 24 to separate at the low trip time or start of the predetermined time interval. It can be seen from FIG. 2 of the drawings that the tang 22 functions as a lever for movihg the bimetal member upwardly when pushed toward the top of the base 12. The tang 22 when pushed downwardly toward the base is permanently deformed or bent. This will insure that when the circuit breaker 10 is subsequently used in an electric motor that it will open up within the predetermined time interval desired. Due to inherent spring back characteristics in the bimetal member 40, the tang 22 is pressed down at the beginning or the start of the low trip time of the predetermined time interval so that the resultant time period at which it will deflect toward its open position, as shown in FIG. 4, will be intermediate the range between l6 and 22 seconds. After the bimetal member 40 is calibrated, the circuit breaker is disconnected from the testing circuit.

From the foregoing, it can be seen that the provision of the tang 24 enables the circuit breaker to be readily and accurately calibrated and that it provides for a method of calibration which is highly accurate.

FIG. 5 shows an alternative embodiment of an overload circuit breaker 60 constructed in accordance with the provisions of the present invention. The circuit breaker 60 is identical to the circuit breaker 10, except that a different shape bimetal member 62 is employed. The parts of the overload circuit breaker 60 which are identical to and correspond to the parts of the circuit breaker 10 have been given the same reference numerals. The bimetal member 62 has a pair of

U-shaped portions

63 and 64 which are integrally connected at the free ends of the upper and lower legs bycross

pieces

65 and 66. The bimetal member 62 also has a lower or secondary portion 68 which is lanced from the upper portion and is integral at its free end with. the

' cross piece 66. The width of the lower portion 68 corresponds to the width between the U-shaped sections 63 and. Also, the bimetal member 60 is secured to the tang 22 by welding rather than by a rivet. The operation and function of the bimetal member 62 is the same as that previously described above in connection with the bimetal member 40.

Although the illustrated embodiments hereof have been described. in great detail, it should be apparent that certain modifications, changes, and adaptations may be made in the illustrated embodiments, and that is is intended to cover all such modifications, changes and adaptations which come within the spirit of the present invention.

What is claimed is:

1 An overload circuit breaker comprising: a metal base; a stationary contact carried by, but electrically insulatedfrom the base; a tang upstruck from said base and bent to a first position in which it is disposed above the plane of said base, said tang being supported in cantilever fashion by said base; a bimetal member including a primary U-shaped portion and a secondary portion, saidsecondary portion having one end connected with one leg of said primary portion and its other end connected with said tang and being supported in cantilever fashion by said tang, said primary portion having a mobile contact adjacent the free end of the other leg thereof which overlies said stationary contact, said bimetal member being self-biased toward a first position in which said mobile contact biasingly engages said stationary contact to provide conductive path therethrough when a current of less than a predetermined magnitude is passed therethrough, said bimetal being movable toward a second position in which it is disengaged from the stationary terminal to break the conductive path therethrough when a current in excess of apredetermined magnitude and for a predetermined time interval is passed therethrough, said tang being bendable relative to said base from its first position to a second position to adjust the biasing force of said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved towards its second position when a current in excess of a predetermined magnitude is passed therethrough can be varied.

2. An overload circuit breaker comprising: a metal base, a stationary contact carried by, but electrically insulated from the base; a tang integral with the base and having a first portion bent upwardly from the plane of the base to form an acute included angle with the base and a second portion bent to extend generally parallel with the base, said tang being supported in cantilever fashion by the base; a one piece bimetallic member including a primary U-shaped portion and a secondary planar portion, said secondary portion having one end secured to the second portion of said tang and being supported by said tang in cantilever fashion, said secondary portion at its free end being integrally connected with one leg of said primary portion, said secondary portion and said primary portion being disposed side by side and said primary portion having a mobile contact at the free end of its other leg which overlies said stationary contact, said bimetal member being self-biased toward a first position in which said mobile contact biasingly engages said stationary contact when a current of less than a predetermined magnitude is passed therethrough, said bimetal member being movable toward a second position in which it is disengaged from the stationary contact to break the conductive path therethrough when a current in excess of a predetermined magnitude is passed therethrough and for a.

predetermined time interval, said tang being bendable relative to said base to an adjusted position to adjust the biasing pressure of said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved toward its second position when a current in excess of a predetermined magnitude is passed therethrough can be varied.

3. in an overload circuit breaker having a base, a stationary contact carried by, but insulated from the base, a bimetal member including a primary U-shaped portion having one leg carrying a mobile contact adjacent its free end and a secondary portion supported in cantilever fashion by said base and having its free end connected with the other leg of the U-shaped primary portion, and in which the bimetal strip is normally selfbiased toward a first position in which the mobile con tact biasingly engages the stationary contact to provide a conductive path through the bimetal member, but which is movable toward a second position inwhich the mobile contact is disengaged from the stationary contact to break the conductive path through the bimetal member when a current in excess of a predetermined magnitude is passed therethrough for a predetermined interval of time, the improvement comprising: an upstruck bendable tang integral with said base and having a first portion extending upwardly from said base and a second free end portion extending generally parallel with said base, said second free end portion being secured to the end of said secondary portion remote from the free end of the latter, said tang being bendable relative to the plane of said base to an adjusted position to vary the biasing pressure exerted by said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved toward its second position when a current in excess of a predetermined magnitude is passed therethrough can be adjusted.

Claims

1. An overload circuit breaker comprising: a metal base; a stationary contact carried by, but electrically insulated from the base; a tang upstruck from said base and bent to a first position in which it is disposed above the plane of said base, said tang being supported in cantilever fashion by said base; a bimetal member including a primary U-shaped portion and a secondary portion, said secondary portion having one end connected with one leg of said primary portion and its other end connected with said tang and being supported in cantilever fashion by said tang, said primary portion having a mobile contact adjacent the free end of the other leg thereof which overlies said stationary contact, said bimetal member being selfbiased toward a first position in which said mobile contact biasingly engages said stationary contact to provide conductive path therethrough when a current of less than a predetermined magnitude is passed therethrough, said bimetal being movable toward a second position in which it is disengaged from the stationary terminal to break the conductive path therethrough when a current in excess of a predetermined magnitude and for a predetermined time interval is passed therethrough, said tang being bendable relative to said base from its first position to a second position to adjust the biasing force of said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved towards its second position when a current in excess of a predetermined magnitude is passed therethrough can be varied.

2. An overload circuit breaker comprising: a metal base, a stationary contact carried by, but electrically insulated from the base; a tang integral with the base and having a first portion bent upwardly from the plane of the base to form an acute included angle with the base and a second portion bent to extend generally parallel with the base, said tang being supported in cantilever fashion by the base; a one piece bimetallic member including a primary U-shaped portion and a secondary planar portion, said secondary portion having one end secured to the second portion of said tang and being supported by said tang in cantilever fashion, said secondary portion at its free end being integrally cOnnected with one leg of said primary portion, said secondary portion and said primary portion being disposed side by side and said primary portion having a mobile contact at the free end of its other leg which overlies said stationary contact, said bimetal member being self-biased toward a first position in which said mobile contact biasingly engages said stationary contact when a current of less than a predetermined magnitude is passed therethrough, said bimetal member being movable toward a second position in which it is disengaged from the stationary contact to break the conductive path therethrough when a current in excess of a predetermined magnitude is passed therethrough and for a predetermined time interval, said tang being bendable relative to said base to an adjusted position to adjust the biasing pressure of said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved toward its second position when a current in excess of a predetermined magnitude is passed therethrough can be varied.

3. In an overload circuit breaker having a base, a stationary contact carried by, but insulated from the base, a bimetal member including a primary U-shaped portion having one leg carrying a mobile contact adjacent its free end and a secondary portion supported in cantilever fashion by said base and having its free end connected with the other leg of the U-shaped primary portion, and in which the bimetal strip is normally self-biased toward a first position in which the mobile contact biasingly engages the stationary contact to provide a conductive path through the bimetal member, but which is movable toward a second position in which the mobile contact is disengaged from the stationary contact to break the conductive path through the bimetal member when a current in excess of a predetermined magnitude is passed therethrough for a predetermined interval of time, the improvement comprising: an upstruck bendable tang integral with said base and having a first portion extending upwardly from said base and a second free end portion extending generally parallel with said base, said second free end portion being secured to the end of said secondary portion remote from the free end of the latter, said tang being bendable relative to the plane of said base to an adjusted position to vary the biasing pressure exerted by said bimetal member whereby the predetermined time interval during which the bimetal is caused to be moved toward its second position when a current in excess of a predetermined magnitude is passed therethrough can be adjusted.